In the graphic arts, it is desirable to produce a color proof to assist a printer in correcting a set of photomasks which will be used in exposing printing plates. The proof should reproduce the color quality that will be obtained during the printing process. The proof must be a consistent duplicate of the desired half-tone or line image, and should neither gain nor lose color. Visual examination of a color proof should reveal the following characteristics:
1. Any defects on the photomask.
2. The best color rendition to be expected from press printing of the material.
3. The correct gradation of all colors and whether grays are neutral.
4. The need, if any, for subduing any of the colors and/or giving directions for altering the film photomask before making the printing plates.
Color proofing sheets for multicolored printing have heretofore been made by using a printing press proof which requires taking all the steps necessary for actual multicolor printing. Such a conventional method of color proofing has been costly and time consuming. Color proofing methods have therefore been developed to simulate the quality of press proofs.
In the surprint type of color proofing method, a color printing sheet is prepared by successively producing images of different colors from different color separation films onto a single receptor sheet. This is done by utilizing a single opaque support and by applying toners, photosensitive solutions or coatings of photosensitive materials of corresponding colors on the opaque support in succession. An example of this approach is described in U.S. Pat. No. 3,671,236. An advantage of the surprint type of color proof is that the color saturation is not influenced by superimposed plastic supports. This method more closely resembles the actual printing and eliminates the color distortion inherent in the overlay system.
Various processes for producing copies of an image embodying photopolymerization and thermal transfer techniques are known as shown in U.S. Pat. Nos. 3,060,023; 3,060,024; 3,060,025 3,481,736; and 3,607,264. In these processes, a photopolymerizable layer coated on a suitable support is imagewise exposed to a photographic transparency. The surface of the exposed layer is then pressed into contact with the image receptive surface of a separate element and at least one of the elements is heated to a temperature above the transfer temperature of the unexposed portions of the layer. The two elements are then separated, whereby the thermally transferrable, unexposed, image areas of the composite transfer to the image receptive element. If the element is not precolored, the tacky unexposed image may now be selectively colored with a desired toner. The colored matter preferentially adheres to the clear unpolymerized material. U.S. Pat. No. 3,574,049 provides a transfer process for printing a design on a final support which comprises (a) printing a design onto a temporary support, (b) superimposing the temporary support and the final support, (c) applying heat and/or pressure to the superimposed structure formed in (b), and (d) separating the temporary support from the final support which retains the printed design. The affinity of the design for the temporary support is lower than its affinity for the final support.
In U.S. Pat. No. 3,721,557 a method of transferring colored images is claimed which provides a stripping layer coated between the photosensitive element and the support. When the photosensitive layer is exposed to actinic light and developed, the more soluble portions are selectively removed to produce a visible image. The image-carrying support is pressed against a suitable adhesive coated receptor member and, subsequently, the carrier support sheet is stripped to accomplish the transfer of the image. A fresh layer of adhesive is applied to the receptor for each subsequent transfer.
One problem with such surprint type proofing systems is the image is vulnerable to damage from its environment, i.e., from fingerprints, scratches, dust and the like.
In order to protect the surface of the surprint proof, it is commonly the practice to laminate to such surface a thin transparent film of polyester or the like, or a layer of photopolymer which may be polymerized by overall exposure to actinic radiation to form a tough, protective membrane. This postexposure requires an additional processing step. These prior practices, however, generally result in the formation of a thick, glossy surface on the surprint which in some circumstances detracts from the desired appearance of the proof. In many instances, for example, it is preferred that the surface of a multilayer proof print exhibit a matte, or non-glossy, texture in order to closely resemble actual printing on stock which lacks a coated or natural sheen.
Various means have been attempted to reduce the glossy appearance of the noted type of surprint proof, yet none has proven sufficiently simple and effective. The application to the surface of the print of powdered pigments, pigmented sprays or lacquers, or aqueous dispersions of pigments, all as mentioned, for example in U.S. Pat. No. 4,286,046, poses problems of expense, cleanliness, and health while failing to provide a matte of acceptable uniformity, texture, and appearance.
The present invention solves these problems by providing a lamination of thin adhesive and antiblocking layers to the surface of the proof. These layers are borne on one or two temporary supports and are then laminated to the proof. The temporary supports are then stripped off. The proof is itself thereby provided with either a smooth or matte finish depending upon the surface topography of the temporary support from which the aforementioned layers were removed.